For numerous years, in view of the proliferation of diseases transmissible by blood, assiduous attempts have been made to market syringes enabling just one injection to be administered and that are fully reutilization-proof.
Though a very large number of propositions have been made, to date none of these has proved fully satisfactory.
It is usually proposed that use be made of units comprising racks formed on the piston of the syringe and cooperating with one or more studs integral with said syringe body, so as to allow relative motion in one direction and to prohibit any motion in the opposite direction.
There has also been proposed, in document EP 0 339 954, a syringe of which the piston bears studs or lugs, whereas the racks are formed on the body of the syringe.
To use these syringes, the piston is pulled outwardly from the syringe body, a rack thus moves before the stud enabling the piston to move outwards, said rack being shaped so as to prevent any return motion of said piston towards the interior of the syringe body. After filling the body of the syringe during this outward pulling movement of the piston, the piston must be rotated through a given angle in order to bring the second rack into relation with the same stud or with a second stud. In this position, the second stud allows the piston to descend to the bottom of the syringe body but prohibits any withdrawal motion of said piston.
When the piston is thus returned to the bottom of the syringe body, it is no longer possible to rotate it about itself and it is also impossible to remove it from said body due to the blocking engagement of the rack and the second stud.
The utilization of a syringe of this type is complex due to the fact that the piston must be made to rotate about itself through a given angle before ejecting the product drawn into the syringe.
There has also been proposed, in document DE 38 33 138, a single-usage syringe of which utilization is, from the user's point of view, perfectly similar that of usual syringes. This syringe has an insert mounted rotatably mobile within the syringe body. The insert can bear either lugs cooperating with racks formed on the piston, or racks cooperating with lugs borne by the piston. One of the racks is slanted at an angle to the axis of the syringe so as to rotatably drive the insert when the piston is drawn out and to bring the rack and lug into cooperation so as to enable the piston to be pressed in.
These arrangements have the drawback of being subject to working poorly as a result of the frictional forces at play between the syringe body and the insert and preventing said insert from rotating.
Furthermore, it has been observed that the single-usage syringes provided usually have a drawback consisting in the fact that, when they are used, the piston must be pulled back to the end of its outward stroke from the syringe prior to performing the manipulations required to enable injection and the second rack to be brought into play.
This invention also tends to provide a syringe enabling the user to perform intermediary dosages, i.e., not to completely draw out the piston before the injection.
This syringe will thus enable the injection of a variable quantity of product, and yet prohibit any further injection thereafter.
Moreover, it has been observed that the utilization of syringes only authorizing one single injection requires, in certain cases, the utilization of two or more syringes for the same treatment.
There are, in fact, a certain number of products of which the utilization requires that a liquid and a powder be mixed together for prior constitution of a solution to be injected subsequently.
This invention thus tends to provide a syringe which, depending on its constitution, will enable a predetermined number of injections to be administered, one in the case of conventional utilizations, or two or more for special utilizations during treatment or laboratory analyses.